In recent years, there has been a demand for an exponential increase in memory capacity of a recording medium such as a hard disk. In order to meet the demand, a magnetic recording medium having high memory capacity is being developed.
In a magnetic recording medium used in conventional hard disks, a predetermined region of a thin film including polycrystals of magnetic fine particles is used as one bit for recording. In order to increase recording capacity of a magnetic recording medium, the recording density should be increased. In other words, it is necessary to reduce the recording mark size which is usable for recording of one bit. However, when the recording mark size is simply reduced, the influence of noise which depends on the shapes of magnetic fine particles becomes nonnegligible. If the particle size of magnetic fine particles is reduced to lower the noise, a problem of thermal fluctuation occurs, which makes it impossible to maintain recorded data at a room temperature.
In order to avoid these problems, a bit patterned medium (BPM) has been proposed, in which the recording material is separated by a nonmagnetic material in advance, and a single magnetic dot is used as a single recording cell to perform read and write.
In magnetic recording media installed in HDDs, there is an arising problem of the interference between adjacent tracks which inhibits improvement in track density. Particularly, reducing a fringe effect of a write head field is a significant technical problem to be solved. To solve this problem, there has been developed a discrete track recording-type patterned medium (DTR medium), in which the magnetic recording layer is processed so that the recording tracks are physically separated from each other. In the DTR medium, it is possible to reduce side erase which erases information in the adjacent tracks in writing and side read which reads information in the adjacent tracks in reading. On this account, the DTR medium is promising as a magnetic recording medium capable of providing a high recording density. Incidentally, it should be noted that the term “patterned medium” as used herein in a broad sense includes the bit patterned medium and DTR medium.
As a method of manufacturing a patterned medium, a technology of forming a pattern of a magnetic region and a nonmagnetic region on a magnetic recording layer by deactivating magnetism of the recording layer has been known. In the technology, it is important to deactivate the magnetism correctly and uniformly on the target region in order to obtain a magnetic recording medium having an excellent pattern.